Correct approach to do what? What is the use case?
Hepatitis can cause an hepatic coma, but that is not a patient-specific fact. It is generic, and should therefore be part of the reference (Vocabularies) tables, rather than in FACT_RELATIONSHIP. ICD-9-CM has that as a pre-coordinated concept composed of two distinct conditions (one a disease of the liver, the other of the brain). For whatever reason they decided to have such a pre-coordination here, but they certainly don’t have all possible conditions that could be linked because one causes the other.
But again: What are you trying to achieve?